Process for the production of hydroquinone

ABSTRACT

Process for the production of hydroquinone by electrochemically oxidizing benzene to quinone and reducing the quinone to hydroquinone. The process involves circulating a finely dispersed recycle stream of benzene and dilute sulfuric acid, which contains no more than 2 percent of quinone related to the benzene, through the anode compartment of an electrolytic cell and a finely dispersed recycle stream of benzene, dilute sulfuric acid and hyroquinone through the cathode compartment of an electrolytic cell whereby the quinone content of the benzene solution introduced into the cathode compartment for reduction is not higher than about 2 percent.

United States Patent 0 1 [111 3,

Fremery et al. M lMarch 20, 1973 [541 PROCESS FOR THE PRODUCTION OF 2,285,858 6/1942 Horrobin et al. ..204/78 HYDROQUINONE 3,663,381 5/1972 Cavity ..204/78 Inventors: Max y; Hermann "fiver, FOREIGN PATENTS OR APPLICATIONS both of Wesseling; Gert Schwarzlose, Bonn Bad Godesberg, n of 117,251 1/1901 Germany ..204/78 Germany [73] A U Rh B unk me Primary Examiner-F. C. Edmundson ssignee: mon einlsche ra o n Kraflstofl Akfiengeseuschafi wes Attorney Arthur Connolly et al. seling near Cologne, Germany 57] ABSTRACT [22] F'led: 1972 Process for the production of hydroquinone by elec- [21] Appl. No.: 226,124 trochemically oxidizing benzene to quinone and reducing the quinone to hydroquinone. The process involves circulating a finely dispersed recycle stream [301 Foreign Apphcamm Pnonty Data of benzene and dilute sulfuric acid, which contains no Feb. 24, 1971 Germany ..P 21 08 623.7 or than 2 percent of quinone related to the benzene, through the anode compartment of an elec- [52] US. Cl. ..204/73 R, 204/78 trolytic cell and a finely dispersed recycle Stream of [5 l 1 B (IL-Con, 29/06 C07: 37/00 C076 49/00 benzene, dilute sulfuric acid and hyroquinone through Field Of Search R, the cathode compamnent f an electrolytic cell whereby the quinone content of the benzene solution [56] References Clted introduced into the cathode compartment for reduc- UNITED STATES N S tion is not higher than about 2 percent.

1,322,580 11/1919 Kitchen ..204/78 X 1 Claim, 1 Drawing Figure ll) 15 Filier Q A PROCESS FOR THE PRODUCTION OF I HYDROQUINONE BACKGROUND OF THE INVENTION anode compartment and cathode compartment of an electrolytic cell separated by a diaphragm in order to keep the concentration of quinone in the benzene at a low level. The hydroquinone is recovered from the electrolyte leaving the cathode compartment, for example by cooling and separating out the hydroquinone crystals formed. Electrodes of lead or lead alloys are generally used, depolarising means for the lead anode having occasionally been used. Dilute sulfuric acid, optionally with the addition of some sodium sulfate is generally used as the electrolyte. Since the electrolyte mixture is a two-phase mixture, emulsifiers were added despite the fact that they can give rise to disadvantages in so far as they may take part in the reaction and have an adverse effect upon separation of the hydroquinone.

SUMMARY OF THE INVENTION The present invention provides a process for the production of hydroquinone by the electrochemical oxidation of benzene to quinone and electrochemical reduction of the quinone to hydroquinone. According to the invention a finely dispersed recycle stream of benzene, dilute sulfuric acid and quinone whose quinone content is no higher than 2 percent related to the benzene is passed at high speed through the anode compartment of an electrolytic cell. Fresh benzene is added to this recycle stream before it is introduced into the anode compartment, removing a corresponding proportion of the anode recycle stream after the anode compartment. The sulfuric acid is separated from this proportion and returned to the anode recycle stream. The residual benzene-quinone mixture containing no more than about 2 percent of quinone is added to a finely dispersed cathode recycle stream of benzene, dilute sulfuric acid, and hydroquinone before it is introduced into the cathode compartment of an electrolytic cell. A corresponding proportion of the cathode recycle stream is removed after the cathode compartment, separating the benzene from this proportion and returning it to the anode recycle stream. The hydroquinone is separated from the residual hydroquinone sulfuric acid mixture, and the acid thus obtained is returned to the cathode recycle stream before it is introduced into the cathode compartment.

DETAlLED DESCRIPTION Theinvention in further illustrated by reference to the accompanying schematical flow diagram, the F lGURE.

A recycle stream of dilute sulfuric acid and benzene containing small quantities of quinone, up to 2 percent related to the benzene, is passed through anode compartment A through pipes l, 2, 3 and 4. It is best to use an approximately 10 to 30 percent, more particularly a percent sulfuric acid, the ratio of benzene to sulfuric acid being between 121 and 1:6. Fresh benzene and unreacted recycle benzene recovered from the process are added to the recycle stream through pipes 5 and 6.

A filter is installed in the pipe 1. By means of this filter, solid secondary products from the anode compartment, such as lead oxid, lead sulfate or sulfonated products of benzene and quinone polymers, are removed from the recycle stream. The rate of flow of the recycle stream is adjusted so that turbulence is maintained in the cell. A Reynolds number of 2,000 should be exceeded in order to mix thoroughly the two liquid phases of electrolyte and organic compounds. Part of the recycle stream, for example from 5 to 30 percent is delivered to separator B through pipe 7.- In the separator B, the sulfuric acid is separated from the benzene solution and returned through pipe 8 to the recycle stream. The benzene solution should contain no more than about 2 percent of quinone. It is delivered through pipe 9 to cathode compartment C. A recycle stream, consisting of dilute sulfuric acid, benzene, and small amounts of hydroquinone is also passed through the cathode compartment C (through pipes l0, ll, 12, 9). The ratio of benzene to sulfuric acid is between 1:2 and 1:8 advantageously between 1:4 and 1:6, where 5 25 percent, for example 10 percent sulfuric acid is used. The hydroquinone content can amount to be between about 5 and 15 percent corresponding to the solubility at the temperatures used. Part of the cathode recycle stream, for example 10 percent, is delivered through pipe 13 to separator D. A smaller or larger proportion of the recycle stream can of course also be removed depending upon the equilibrium. In the separator D, the recycle benzene containing only very small quantities of hydroquinone corresponding to the solubility, for example 0.1 percent, is separated from the sulfuric acid solution. It is returned to the process through pipe 6. The sulfuric acid solution containing the hydroquinone is delivered through pipe 14 for recovery of hydroquinone in E, for example by crystallization at low temperatures, optionally under reduced pressure. The sulfuric acid containing dissolved hydroquinone is returned through pipe 15 to the cathode recycle stream. The mother liquor from the crystallization can also be introduced there.

In general by conducting the electrolysis low temperatures are "preferred, i.e. 20 to 60C. If desired, electrolytic cell having a diaphragma of conventional material separating the anode from the cathode may be used. Also, anodes and cathodes of conventional material may be used, although titan clad with lead dioxide is preferred. The electrolytic cell may be operated in an usual manner, the current density and the quantity of electricity being maintained over a wide range.

By using the two circuits, the process can be made very simple pertaining to apparatus used. The hydroquinone obtained is very pure because no impurities from the anode compartment enter the cathode recycle stream.

The following example further illustrates the invention.

EXAMPLE A mixture of 9 liters of benzene containing 1.5 percent of quinone and 18 liters of 20 percent sulfuric acid was passed as recycle stream through an anode compartment of an electrolytic cell with a volume of approximately 2 liters. Electrolysis was carried out at 7.5 V, 600A and 35C. Part of the reaction mixture obtained, having a quinone content of 2 percent, was added to the recycle stream passed through the cathode compartment consisting of approximately 20 liters of percent sulfuric acid, 7 liters of benzene and small quantities of hydroquinone. The hydroquinone concentration rose to approximately 80 g/l in the cathode compartment. A proportion of the reaction mixture thus obtained corresponding to the benzene solution delivered to the anode compartment was removed and separated into a benzene solution and a sulfuric acid solution. The benzene solution containing approximately 0.015 percent of quinone and 0.15 percent of hydroquinone, was returned to the anode compartment. At the same time, a quantity of fresh benzene corresponding to the benzene reacted was delivered to the anode compartment. l-lydroquinone was recovered from the sulfuric acid solution by crystallization at 0C. The residual sulfuric acid which still contained approximately 35 g/l of hydroquinone was returned to the recycle stream passed through the cathode compartment. The hydroquinone obtained was 99.5 percent pure. The yield based on the benzene used was 5.2 percent, and the current efficiency based on hydroquinone 37.5 percent.

What we claim is:

l. A process for the production of hydroquinone by the electrochemical oxidation of benzene to quinone and the electrochemical reduction of quinone to hydroquinone, which comprises passing a finely dispersed recycle stream of benzene, dilute sulfuric acid and quinone whose quinone content is no higher than 2 percent related to the benzene, at high speed through the anode compartment of an electrolytic cell, passing a finely dispersed recycle stream of benzene, dilute sulfuric acid and hydroquinone, substantially free of quinone, at high speed through the cathode compartment of an electrolytic cell, removing a part of the anode recycle stream after the anode compartment, adding a corresponding amount of benzene to the anode recycle stream before it is introduced into the anode compartment, separating the sulfuric acid from the said part and returning it to the anode recycle stream, adding the residual benzene quinone mixture containing no more than about 2 percent of quinone, to the cathode recycle stream before it is introduced into the cathode compartment, removing a corresponding proportion of the cathode recycle stream after the cathode compartment, separating the benzene from this proportion and returning it to the anode recycle stream, separating the hydroquinone from the residual hydroquinone-sulfuric acid mixture and returning the sulfuric acid to the cathode recycle stream before it is introduced into the cathode compartment.

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